The field of the invention is separation of hydrocarbon gas.
Propane is a valuable component in industrial gases and various processes are known in the art, including processes based on cooling and refrigeration of gas, oil absorption and refrigerated oil absorption, and especially cryogenic expansion processes. However, all or almost all of them suffer from one or more disadvantages.
For example, in U.S. Pat. No. 4,157,904 to Campbell (Jun. 12, 1979), a process for propane recovery employs a cooled feed gas stream that is partially condensed, subsequently expanded to a lower pressure, and then separated in a distillation column. The separation is improved by combining the condensed liquid with a stream having a lower bubble point with cooling of one or both streams prior to expansion. Campbell""s recovery process advantageously increases the overall energy efficiency, however, requires at least in some configurations additional material translating to increased plant construction costs.
In another example, U.S. Pat. No. 4,854,955 to Campbell et al. (Aug. 8, 1989), a process for recovery of propane includes dividing a hydrocarbon stream into first and second streams and subsequent condensation and expansion of the first stream, which is then heat exchanged with a column reject from the distillation column. A portion of the partially condensed column reject is refluxed to the distillation column. Although Campbell""s configuration tends to increase the recovery of propane, the inlet feed gas is typically restricted to dried feed gas.
In a further example, U.S. Pat. No. 5,890,378 to Rambo et al. (Apr. 6, 1999), a configuration for improved propane recovery is described in which much of the equipment required for providing reflux for the absorption section is eliminated while maintaining relatively high propane yields. Although Rambo""s configuration generally reduces equipment related costs to at least some degree, the treatment of a vapor phase feed gas stream and a wet liquid from the feed gas typically require separate processes involving significant amounts of equipment.
Although there are various processes known in the art, all or almost all of them suffer from one or more disadvantages. Therefore, there is still a need to provide improved methods and apparatus for high propane recovery.
The present invention is directed to methods and apparatus for improved propane recovery. In particular, a propane recovery plant has an absorber column.that receives a feed gas, and that produces a cold reject vapor and a product fluid. A second column receives at least part of the product fluid in a gas form, and the second column is further fluidly coupled to a condenser that forms a reflux condensate by using at least in part the cold reject vapor as a refrigerant. It is generally contemplated that a first portion of the reflux condensate is recycled into the second column, and that a second portion of the reflux condensate is fed into the absorber column.
In one aspect of the inventive subject matter, the second column comprises a deethanizer column, which may further include an integral water removal contactor, especially when the deethanizer further receives a wet liquid feed gas. Where an integral water removal contactor is utilized, preferred scrubbing agents include triethylene glycol.
In another aspect of the inventive subject matter, the condenser is preferably an integral overhead condenser that may employ propane as a refrigerant. While contemplated methods and configurations are generally contemplated to improve propane recovery, it is particularly contemplated that the recovery is up to 99 mol %, and where propane is employed as a refrigerant it is contemplated that the recovery is up to 99 mol %.
In a further aspect of the inventive subject matter, a feed gas separation element receives a wet process gas, and produces a wet gaseous feed gas and a wet fluid feed gas. A deethanizer column receives the wet fluid feed gas, wherein the deethanizer column comprises an integral water removal contactor, and wherein the deethanizer column further comprises an integral overhead condenser that forms a reflux condensate, of which a first portion is recycled into the deethanizer column and of which a second portion is fed into an absorber column.
In a still further aspect of the inventive subject matter, a method of improving the recovery of propane from a feed gas has a step of providing an absorber column, and a deethanizer column with an overhead condenser that utilizes at least in part a cold reject vapor from the absorber column as a refrigerant, wherein the overhead condenser produces a reflux fluid. In a further step, a first recycling loop is formed in which a first portion of the reflux fluid is recycled into the deethanizer column, and in another step a second recycling loop is formed in which a second portion of the reflux fluid is fed into the absorber column. In yet another step, a third recycling loop is formed in which a product fluid from the absorber is fed into the deethanizer column in a gaseous form.